Construction of cams



Feb. 6, 1,945. F B HALFORD ETAL 2,369,043

CONSTRUCTION OF CAMS Filed Aug. 3, 1943 t orne Patented Feb. 6, 1945 UNITED STATES PATENT oFFlcE CONSTRUCTION or oAMs Frank Bernard Halford, Edgware, John Longmuir Penman Brodie, London, and Robert Miller, Edgware, England, assignors to The -De 'Havilland' Aircraft Company Limited, Edgware, Middlesex,England, a company of Great yBritain Application August 3, 1943, Serial No. 497,241

v In Great Britain October 6, 1942 v2 claims. (ol. :za-iis) In the method of construction according to thisr invention the master cam is built up of asuitable number of separate sections connected by dowels and all keyed on a mandrel, each section which is -constituted by a circular or other disc blank of suitable initial thickness having this thickness reduced by cutting away the metal on one face so as to leave a raised part the peripheral contour of which has the shape which that part of the cam is to have, all these sections being next assembled on a mandrel and the excess metal removed down to the shaped edges of the raised parts lying between adjacent sections, after which the sections are separated and the raised part on the one face of each is removed leaving both faces flat and parallel, the sections being next and nally assembled on the mandrel and the surface of the whole cam as thus built up finished off. This finishing as also the removal of the excess metal when the blanks are rst assembled may be elected by suitable means for example either by grinding, turning or by hand work. In the shaping of the raised part on the one face of each section and for the removal of the metal necessary to effect this shaping `there may be used an engraving machine or a machine of like type and this is employed in association with a pantagraph copying apparatus. The necessary contour is thus takenA and reduced from hand-made templates which have been made several times thefull sizeof the cam. In the finished process' when the sections have been finely assembled there will be removedany slight steps over the surface of the Whole cam which may occur where the faces of the sections abut and as a result of theremoval of the raised metal from the face of each section.

By this process a single `lobe master cam can be made, but it is possible in the same way to form a cam having two or even more lobes as may be required. Where, however, it is desired to produce say a number of such master or form cams, it is preferable to make rst a single lobe master cam asvdescribed above and then with the aid of this to shape each formcam first as to one of its lobes and then by relative rotation of the master cam and the form cam to shape the second lobe of the latter. j

By way of example the accompanying drawing illustrates the improved method of constructing a'cam and in particular a master cam which is more especially intended for use in the shaping of turbine blades. In this drawing:

Figure 1 shows in perspective one of the discs or blanks from which the complete vcam is ybuilt up this disc having been subjected to the first had its thickness reduced by the removal of the superfluous metal from the one face.

vFigure 5 is an end view of the finished cam.

Figures 6, 7, 8 and 9 are side elevations of parts of two adjacent discs illustrating on an enlarged or exaggerated scale the several stages in the process.

Figure 10 is a side elevation of a single lobe master cam as it may be arranged for the formation of a two-lobed form cam.

Figure 11 is an end view of such a two-lobed cam. i

In the rst place there are taken a suitable number of similar circular discs of such thickness as may be desirable. In some cases all the discs may have the same thickness, but in other cases it may be convenient vfor some of them to be thicker than others and in the same way the diameters of all the discs may be the same or may differ. Each such -disc A as seen in Figure l has through it a hole B for the mandrel on which the assembled discs are mounted, `and two holes C for dowels, and in the hole B is a keyway B1 to permit of fixing the disc section onthe mandrel. Each disc or blank has initially a, thickness which is slightly greater than the section of the cam constituted by the disc will have finally so that when these discs are first assembled on the mandrel D as seen in Figure 2 the overall length of the body formed by them will exceed the length which the linished cam Ais to have. can be seen by comparing the length of the builtflat face 'of the'next adjacent disc A4. cess metal fromnthe perip'heri'es of the assemup body as shown in Figure 2 with the finished cam as shown in Figure 4. The excess thickness of each blank may be of the order of .02 inch,- but may be determined as found desirable,

Each individual disc A is subjected to a process by'which there is removed from its 'one .face a layer of metal of uniform thickness over such marginal or other part of the face as will resultV -j in there remaining a part A1 which projects from the at face part A2 around that part A1. This between the sections isshown in Figure 9 where the diameter at the junction will be seen to be the same as the diameter of the projection -part A1 as seen in Figures 6 and '7. The complete camwill nowhave the correct overalllength. e

. Such a master cam may be used in the production of a form cam by suitable means as for instance by mounting the master cam and the blank for the form cam on al mandrel which is rotated so as to keep the master cam in contact with a follower while the blank isacted on by a grind- 4 lobe.

be the excess thickness which was originally pro-Y vided in the blank, that is to say, for example andas mentioned above, this part may project about .0 2 inch.v necessary to giveY the edgeA3v of the projecting In the removal of the metal part A1' the correct'contour the latter may be produced by a pantagra'ph' from yoversize templates'v which have been carefully made vby hand, an engraving or like machine being used which will rtake ol the unnecessary metal and leave the edge A3 of the projecting part and the surround-f ing surface A2r reasonably smooth.

The lgrinta-ns constituted by the discs A are now assembled on. themandr'el D' and they will then appeanas `shown in Figure 2, as a cylinder the surface of which is interrupted at spaced intervals by a. series of annular grooves E the depth of which will vary'overdiierent parts of the circumference land will be different as between separate grooves; Each of these grooves, as may be seen in the enlarged view in Figure 6,/is formed as to its sides Von the one hand by the surface A2 on the face of one disc around the projecting part A1, whose. edge A3 forms the bottom. of' the groove, and on the other hand by the untouched The exbled discs is now removed by rough machining fol'- lowed by hand lfinishing, as' by filing andscraping, whichfis necessary havingregard to the shape` which'the' nished cam is to have at different points along it approximately to the contours of K The body at thisv length 'overall ity Will' be longer than is required forY l the finished cam. l l

'The next stage is to take 4allthe disc sections on fromv the mandrel and separate them and from the face' of each of'ythem'there is then removed the whole-of thel shaped projecting partv A1 so that the section is left with both its faces flat and par,-

allell to enable them tor but't up'smoothly against lthe faces-'of the next adjacent sections. The sectionsare now assembled once more and this time permanently on the mandrel and yany slight steps betweenthe sections, such as shown in an exaggerated form in Figure `8 between the. abuttingv edgesA of the adjacent sections, are taken off by grindingor otherwise andthe surface of the whole cam is finished. In this state it isshown inFigures4 andl.5 and the appearance (of, the, junction ing, wheel Aor tool.

In the `above description in reference to the drawing -it has been assumed that the master cam to bel made' has a single lobe, but it is to be understood that by employing a similar process it is possible to make such a cam ywith more than one In the production from a master cam of a forml cam with ysay two lobes it is preferable to construct the master. camwith only one lobe and use this inv shaping the form cam with its two lobes. This may be done by first shaping the one Apart of the blank which is to be the form cam with other part of the blank' to form -the second lobev is then carried out. In certain cases, however, according to the purposeV for which the form cam is to be used it may be desirable to arrange for the operative lobesor parts of thev form camto be set out somewhat radially with respect to the cam axis. fected in the following way and as shown in FiguresjlO andrll. The master cam A5 is identical inform with that shown in Figures 4 and 5 and comprises a lobe portion" A6v of complex form, which happens tojbe shown uppermost .in Figures 4 and 5, but lowermost in Figure l0, together with a'base part of suitable shapeA which, for exvample, may be mainlycylindrical since it does not aie'ct the inal shape' of the part to be copied from the master cam whetherthis is a work piece or'a two-lobed form cam G as shown in Figure l0. Themaster cam A5r and' the blank Gxwhich is to be the lform cam are respectively mounted on parts D1 andv Dzlof a mandrel kwhich are relatively eccentricthe part D'beingoiiset with respect to the part Dl.- yThe formV camI G has two lobes G2 'and Gi; eachidentical with the part A6 of the'master' cam, but each situated at a greater distance from the axis about 'which the camG is' then rotated 4 at G3i The second lobe`G4 is then' formed leaving" only the blending `ofthefmetal between the lobes at the points `CJran'd" Gto be carried out by hand operation.4 This two-lobeolform'v camV will then" beready for use' when' rotated'about `its true centre. In Figure 11 'the' outline of the original blank is "indicated atG'I and that offthe parts before nalshapin'g` is indicated at G3.

What we claimI as our inventionv and desire to secure by Letters Patent is: j n

l. The` herein vdescribed"-methodv of making a cam comprisingy the steps of building, up a series of separate sections connected together and keyed on a common mandrel in which each section'.v is initially a 'disc-'like member having on one flat face a slightly raised part whose' peripheralcontour isthat to beV givefz'iltol the Apart ofthe nisled The shaping of the form cam may be efcam to be constituted by that section, and wherein all the sections when assembled as a body on the mandrel first having metal removed from their peripheries so as to bring them respectively to the contours of the vraised parts on their faces, and then removing these raised parts thereby reducing the thickness of the' several sections sov that when they are again assembled on the mandrel the ,cam thus built up will havethe desired overall length.

2. The herein described method of making a master cam from which form cams can `be reproduced comprising the steps of buildingl a number of separate sections mechanically connected and all keyed on a common mandrel, each section being constituted by a disc-like member of suitable initial thickness and having this thickness reduced by cutting away the metal on one fiat face so as to leave thereon a raised part the peripheral contour of which has the shape which that part of the cam is to have, assembling al1 of thesesections on a mandrel and removing the excess metal down to the shaped edges of the raised parts lying between adjacent sections, separating the sections and removing the raised part on the one nat face of each section leaving both facesflat and parallel, and assembling the sections on the mandrel and iinishing off the surface of the whole cam as thus built up.

FRANK BERNARD HALFORD.

JOHN LONGMUIR PENMAN BRODIE.

ROBERT MILLER. 

